This invention is directed to a turbo-machine and in particular to the provision of an integrated scroll case distributor for use with machines of the type including pump-turbines.
In previous arrangements of conventional reaction type turbines and pump-turbines the volute shaped scroll casings have been provided with an internal stay ring comprising an annular array of guide vanes for the purpose of maintaining the sectional shape and integrity of the scroll, and to direct the passage of liquid in relation to the slot-like opening of the distributor to which the scroll casing connects. In some instances these guide vanes have been arranged in the stay ring of the scroll case in such a manner as to place certain portions of the vanes under high tension, while other portions of the vanes have been under compression.
In the type of improved design, as shown in Canadian Pat. No. 882,490 issued Oct. 5, 1971, Piguet, the points of attachment to the scroll case are made at the centers of the stay vanes, so as to substantially uniformly stress the full cross-section of the vanes in tension. Thus, is existing turbo-machines it has been general practice to provide the scroll casing with a stay ring, to provide constraint by its vane members acting in tension so as to withstand the opening force exerted by hydraulic pressure, which tends to deform the scroll casing so as to enlarge it, tending thus to spread its edges apart.
The adjoining structure, the distributor, to which the scroll casing is attached in the prior art, provides a flow mouth, connecting with the runner of the machine, and having the wicket gates located between the opposed lips of the distributor. Lindquist, Canadian Pat. No. 726,482 issued Jan. 26, 1966, utilizes the wicket gates to absorb hydraulic defomation forces acting on the distributor.
The present invention combines the structure of the distributor as an integral part of the scroll casing, thus providing a scroll casing having a distributor portion integrally combined therewith, having a single series of stay members in the casing, wherein the integrated components of the distributor are adapted to provide a tensile or tying function to the structure of the scroll casing. A sleeve around each of the tying members can transmit compressive forces from the generator if so desired.
In accordance with the present invention the scroll stay ring is dispensed with, the distributor is structurally combined with the scroll casing and the requisite holding tensile force necessary to maintain the form of the scroll and the slot-like passage of the distributor at its predetermined opening is provided by tensile bolts. These bolts may be pretensioned and also may be used as the pivots on which the wicket gates are mounted. Pretensioning is accomplished in one instance by use of a compression sleeve about each bolt, against which the scroll case is compressed by the tensile load of the bolt.
By providing a volute casing have an upper distributor ring and a lower distributor ring each concentric with the polar axis of the machine and secured to the respective edges of the scroll case, the two rings provide by their opposed faces a pair of radially inwardly extending lips defining the mouth of the flow slot. The load-bearing tension members, such as bolts, extending between the two rings, are spaced around the volute, each transferring tensile load from the bolt to the scroll by way of the distributor ring portion of the scroll casing, while permiting the removal of individual ones of the bolts, at shut-down.
In the case of pump-turbines, having adjustable wicket gates, the bolts may be located as the pivot for the wicket gates, the gates being suitably modified in cross-sectional profile to accommodate the larger diameter pivot. In such an instance one solution is for the tie bolts to be connected in compressive relation with the slot lips by way of thrust bearings, somewhat in the fashion adopted by Lindquist, above, in his distributor. This permits pivotal rotation of the bolts while maintaining a tying force against the casing lips, to prevent opening up under the effects of hydraulic pressure acting against the casing.
An alternative arrangement of the tensioned load-bearing tie members utilizes an extended tie bolt having a bridging piece supported on external lug portions of the scroll lips, to transfer the load from the tie bolt to the scroll casing, while permitting use of a substantially unstressed wicket gate, thereby obviating the need of heavy duty thrust bearings to transfer load between the wicket gate and the scroll lips. This also utilizes the tie bolt in non-rotative relations, as a stationary or "dead" axle for the wicket gates.
The present invention may be incorporated into high head or low head machines, resulting in more compact, lighter machine structure, while elimination of the stay vanes can be used to modify the machine efficiency characteristic to a more desirable, less peaky characteristic providing a broader load range of high efficiency performance.
Preliminary calculations give indication that a saving in weight due to adopting the improved arrangement can amount to about 26% of the estimated total turbine weight, while a decrease in scroll outside diameter in the order of 5-6% can typically reduce the ratio of scroll diameter to throat diameter (draft tube width) from a value of 3.44 to a value of 3.3, approximating to a 4% reduction in ratio.
A further advantage of the present invention is the significantly diminished space requirements which can be of particular value in some projects.